Vaccines are the most effective means for preventing and even eliminating infectious diseases. Although there are a number of efficacious vaccines based on full pathogens, development of safer more potent and cost effective vaccines based on portions of pathogen (subunit vaccines) is important. During the last two decades several approaches to the expression (bacterial, yeast, mammalian cell culture and plant) and delivery (DNA, live virus vectors, purified proteins, plant virus particles) of vaccine antigens have been developed. All these approaches have significant impact on the development and testing of newly developed candidate vaccines. However, there is a need for improving expression and delivery systems to create more efficacious but safer vaccines with fewer side effects. Some of the desired features or future vaccines are (a) to be highly efficacious (stimulates both arms of immune system), (b) to have known and controlled genetic composition, (c) to have time efficiency of the system, (d) to be suitable for expression of both small size peptides and large size polypeptides, (e) to be suitable for expression in different systems (bacteria, yeast, mammalian cell cultures, live virus vectors, DNA vectors, transgenic plants and transient expression vectors), and (f) to be capable of forming structures such as aggregates or virus like particles that are easy to recover and are immunogenic.
Thus, there is a need for novel carrier molecules for engineering, development and delivery of efficacious subunit vaccines. These carrier molecules should provide advantages and flexibility for: expressing commercially sufficient quantities of target polypeptide in different systems, economical recovery of target polypeptides from source material, accommodating different size (4 amino acids and higher) polypeptides, accommodating tandem repeats of target polypeptides, providing enhanced immune function, use as a high throughput screening tool, and use as a delivery tool for vaccine antigens and disease markers.